/gamemode spectator GUI rework

It is a lesser known fact, that in vanila minecraft in spectator gamemode, a "Spectator Menu" can be accessed by pressing any of inventory slots keys (default 1 through 0) or middle mouse button.

The default features of this menu are very lacking in functions.

- Teleport to a player (Default menu position: slot 1)

- Teleport to a member of a team of your chose (only to players though. So no entities) (Default menu position: slot 2)

What I think should be added to this menu:

- Jump dimentions: teleport to current position in another dimention (if alloved by server.properties) (or position × 8 if to nether)

- Highlight players: already in the game. The deffault key for this action is: "not bound"

- Cinematic camera: already in the game. The deffault key for this action is: "not bound"

- Set Flying speed: can be done through a scroll whell, but unprecise and a handicap to gamers without a mouse

- Toggle Flying

- /trigger: so map creators can choose if they want /trigger objectives to be accessed through this menu. Possible syntax could be "/scoreboard objectives modify objectiveName spectatorMenuAvaidable true" and "/scoreboard objectives modify objectiveName spectatorMenuIcon minecraft:grass_block"

the /trigger menu option could be used for multiplayer maps, like a remake of "Project Winter". In PW (you can find it on Steam), after you died, you can heal, warm, or feed other players through a menu similar to the Minecraft Spectator GUI. So this system could definately be used.